1. Field of the Invention
The present invention relates to an image forming apparatus forming an image on a sheet of recording paper and, more specifically, to a technique of avoiding wasteful stapling in an image forming apparatus having a post-processing apparatus (finisher) performing hole punching process (forming punched holes) and staple binding process.
2. Description of the Background Art
Conventionally, a post-processing apparatus (finisher) capable of automatically performing staple binding (hereinafter also referred to as stapling or stapling process) and hole punching (hereinafter also referred to as punching or punching process) after image formation on recording paper by, for example, electro-photography is sometimes attached to an image forming apparatus. In the stapling process performed in the image forming apparatus, a bundle of paper is bound by using staples, and sets of recording paper bound by staples are successively stacked on a discharge tray.
When sets of recording paper are bound by staples, each set is stapled at a preset same position or positions. When all sets are bound and discharged to the discharge tray, the staples are at the same position. As a result, part of the recording paper stacked set by set rises high. Consequently, the number of stacks that can be placed on the tray becomes smaller and work efficiency lowers, or a staple on a set of recording paper that is being discharged may be caught by a staple of the last discharged set of recording paper, causing discharge failure or irregular stacking. In the following, a mechanism (apparatus) performing the stapling process will be referred to as a stapler.
Japanese Patent Laying-Open No. 4-37592 ('592 Reference) discloses a finisher as a solution to such a problem. In the finisher, successively fed sheets of recording paper are aligned and stopped, and stapled at one or a plurality of positions using one or a plurality of staplers. The finisher includes: a stapler moving mechanism for moving the stapler along the lengthwise direction of a staple binding the sheet of recording paper; a staple position change control mechanism for moving the stapler by a prescribed distance for every set of recording paper to be stapled by using the stapler moving mechanism so that the present staple position is made different from the previous staple position; a recording paper feeding mechanism discharging the sheets of recording paper staple-bound at different positions by the staple position change control mechanism to a discharge tray; and a paper amount setting mechanism lowering top surface of the discharge tray in accordance with the amount of recording paper fed by the recording paper feeding mechanism, so that the top surface of discharge tray is always kept at a constant position.
The finisher binds sets of recording paper with stapler position shifted set by set. Thus, a plurality of sets can be stacked successively with binding positions not overlapped with each other. This realizes better stacking performance of recording paper, and as compared with the prior art, discharging efficiency can be improved.
In a post-processing apparatus capable of punching and stapling, if binding position for stapling is set, it is possible that options for the punching position interfere with the binding position for stapling. By way of example, when holes are punched on a longer side of A4-sized recording paper and the longer side opposite to the punched side or a shorter side is stapled, filing using the punched holes becomes impossible. Noticing such a problem, the user must change the position for staple binding. If it is necessary to first cancel setting for punching other than stapling and then to change setting of staple binding position, the operation could be very complicated.
Japanese Patent Laying-Open No. 2006-154416 ('416 Reference) discloses a controller for an image forming apparatus solving such a problem. The controller controls an image forming apparatus that forms an image on an image recording sheet in accordance with settings. The controller includes: a setting input mechanism allowing an operator to input setting related to image formation in the image forming apparatus; and a setting changing mechanism for changing, in a manner linked with a change of setting of a first setting item by the setting input mechanism, setting of a second setting item different from the first setting. The changed setting of the second setting item as well as the changed setting of the first setting item are applicable to image formation in the image forming apparatus.
If the setting of the first setting item is changed, the setting of the second setting item is changed appropriately by the controller and, therefore, setting can easily be changed.
According to the prior art, when staple binding at two positions is set and punching is set additionally, a bundle of recording paper (a set of recording paper) is bound by staples at two positions and then punched holed are formed. When punching is set, it follows that the bundle of recording paper on which images are formed is filed, for example, in a 2-hole or 4-hole file-binder. Therefore, the simultaneously set stapling may not be permanently necessary. In other words, stapling may be just a temporary or a makeshift means to prevent the bundle of recording paper from going apart before filing.
According to '416 Reference described above, the sheets are staple-bound at two positions and thereafter punched. It may be the case that for only a temporary or makeshift binding, stapling is done at two positions, or wasteful stapling takes place. As a result, staples are wasted and the power is wasted by the stapler. Further, stapling at two positions may limit the range of position shifting when the stapling is done with staple positions made different as disclosed in '592 Reference.